spring steel they are made from is tempered to allow
sharpening with files.
They are usually taper
ground in two dimensions, so the blade’s cutting edge is
thicker than the back, and both the back and the cutting
edge taper from the saw’s heel to the saw’s toe.
The thinner the cutting edge, the greater the taper, and
the higher the polish, the higher the saw’s quality, as
taper results in less set required for the teeth, aided
by the steel’s polish that inhibits binding in the cut.
All these features allow for a narrower kerf requiring
less sawing effort.
There are two fundamental choices in manufacturing a
thin saw that won’t kink. The least expensive
choice is to make the saw stiff by using hard steel and
disposable blades, because such saws can’t be
economically re-sharpened. The second choice is to
temper the saw so that it can be filed, and to stiffen
it by tensioning the blade using hammer and anvil.
When a thin blade is struck on an anvil by a
convex-faced round hammer, a dimple is created; often so
small it can’t be seen by the eye. Steel from the
area around the dimple is pulled inwards toward the
point of impact, making the steel in the circular area
radiating from the dimple stiffer, or “tensioned” on its
Hundreds of such hammer blows applied in
certain patterns equally to both sides of a handsaw
blade can make it stiffer, can true a warped circular sawblade, or can dish a large bandsaw blade to conform
to its wheels while at the same time tensioning the
Truing sawblades are not low-order skills,
and the major saw factories and filing shacks of logging
camps and commercial sawmills was where you found them.
Today it’s largely done on computerized machines, except
for hand saws. Here you either find an old, retired saw
doctor who worked for a big mill, a Japanese saw maker
still tensioning by hand, or are on your own because
there are few references. I’m not going to make a saw
doctor out of you today. But I can get you started with
some basics to practice with on old sawblades.
This old saw has a 3/8” kink in the area marked in
chalk, and before I do anything else to rehabilitate the
saw, I’ll remove this kink and true the cutting edge.
The first step is to remove the handle and bend the
blade using your hands in as complete a circle as
possible… in both directions. This relieves any
recent stress put in the saw, and sometimes makes the
existing kink worse or reveals additional problems like
bow or twist.
The tools I’ll use to remove the kink are a steel anvil
and two hammers, both heavy and light, both with
slightly convex faces. I’ll mark the areas to be
struck with chalk and using and oily rag, keep all steel
surfaces clean and oiled to prevent marking the blade.
Removing a kink or bow
requires stretching the steel surface on the concave side of the
kink, and compressing the surface on the convex side.
Before doing either, the saw’s tension at the cutting edge needs
to removed or my attempt may make the kink worse.
I accomplish this on the concave side by striking along
a line running an inch or slightly less upwards from the
tooth gullets. Each “X” represents two light
hammer hits. I made identical chalk marks on the
opposite side of the saw, but I don’t attempt to strike